A typical gamma ray or scintillation camera such as described in U.S. Pat. Nos. 4,859,852, 4,584,478, 4,095,107, 4,228,515, 4,593,198, 4,782,233, 4,831,261, 4,837,439, and 5,021,667 uses a collimating device which acts as a lens to project onto a position detector a shadow of parallel, converging or diverging gamma rays from a radioisotope tracer in a patient's body. The position detector includes a scintillation crystal coupled to an array of photodetectors and associated position analysis electronics including, for example, a computer. Initially in planar cameras the collimators were made by stacking corrugated sheets alternately inverted to create a multiplicity of collimator holes in the collimation direction generally transverse to the stacking direction. An adhesive such as epoxy is used to attach the layers to each other. The collimator holes may have any desired cross-sectional shape, e.g., square, triangular, hexagonal, round.
With the advent of circular or ring gamma ray cameras the same stacking technique was used, but the stack was made with a cylindrical jigging surface against one face of the collimator stack so that while the corrugated plates continued to be stacked one on top of the other, the two faces of the stack defined a curved cylindrical surface.
Ring cameras normally use three or more arcuate collimator segments per collimating ring to obtain multiple views from which to reconstruct the image tomographically. These collimator rings may have parallel, converging, or diverging collimator holes and the directions of the holes may vary from segment to segment and/or layer to layer in the collimator, i.e., both in the plane of the cylindrical axis and circumferentially. While this construction technique does maintain good alignment of the collimator holes in the plane of the plates, the plates are often misaligned so that the planes of the various plates do not have the same desired parallelism, convergence, or divergence. This causes degradation in image resolution in the transaxial plane of the camera, which is particularly problematic in conventional high-resolution three dimensional cameras. This technique is also quite labor-intensive and expensive to implement because each of the collimator segments is independently fabricated and then must be mutually aligned with the others and assembled. Further, these arcuate segments are easily deformed to depart from their ideal curvature during extensive handling in fabrication of the arcuate segments, shipping, and final assembly of the segments into a cylindrical (annular) ring collimator. An even more important problem is the difficulty in precisely aligning during assembly each of the segments relative to the others in their orientation about and in the plane of the axis. Fabrication of collimator segments by this technique of stacking in the circumferential direction requires a corrugated plate for each hole about the circumference of the collimator ring and this is usually quite a large number. In the general case the collimator is much larger in circumference than in its axial extent.
In another approach the curvature of the segments is achieved by stamping arcuate, often crescent-shaped corrugated sections and stacking them alternately inverted to create the collimator holes running in the direction between the crescent-shaped curved edges. These crescent-shaped plates are stacked in the axial direction, i.e., along the axis of the cylindrical collimator ring, to form a cylindrical arcuate collimator segment. This approach reduces the number of corrugated plates used if the collimator ring employs only a few segments, and thus reduces the labor and time in fabricating a particular collimator ring. This approach also improves the transaxial alignment of the collimator holes because all the corrugations for a segment plate are formed by the same forming operation. But there still remains the problem of misalignment of the plane of the plates with the desired parallelism, divergence or convergence. There also remains the problem of mutual alignment of the collimator segments at assembly so that each segment is precisely aligned relative to the other segments in their orientation about the collimator axis. And these segments too are susceptible to deformation of the curvature during handling in fabrication, shipping and assembly.